Final answer:
Secondary treatment in wastewater management can be aerobic or anoxic, using microorganisms to remove biological matter. This process is true, as it can utilize oxygen (aerobic) or occur in environments without oxygen (anoxic).
Step-by-step explanation:
The statement that secondary treatment may be aerobic or anoxic is A) True. Secondary treatment involves the removal of dissolved and suspended biological matter, which is typically done using microorganisms in a controlled environment. The process can be aerobic, using oxygen and aerobic bacteria to consume organic components through processes like suspended growth systems using "activated" sludge; or it can be anoxic, in which denitrification occurs where nitrogen compounds are reduced, typically without the presence of oxygen.